The gas generators of this type include the one having a housing construction of the so-called single cylinder type and the one having a housing construction of the so-called double cylinder type. These housing constructions include a welded one and a friction welded one. Either of these two types of gas generators have the following fundamental construction. That is to say, these gas generators have a housing formed by a side cylinder having a plurality of gas exhaust openings; an upper cap closing an upper end of the side cylinder; and a lower cap closing a lower end of the side cylinder. The housing contains therein an igniter, gas generating agents, and a cooling/filtering member, which are arranged in this order from the center of the housing in a radially outward direction. The cooling/filtering member is formed to enclose the gas generating agents, extending from the upper cap side to the lower cap side.
In the gas generator having this fundamental construction, pressure of the gas generated in the housing rises instantaneously to inflate an air bag at the time of activation of the gas generator, according to the types of gas generating agents or burning conditions. As a result of this, looseness may occur in both end portions of the cooling/filtering member in abutment with the upper cap and the lower cap, then degradating the hermeticity of the cooling/filtering member at the ends abutting with the upper and lower caps, and as such may cause the slag in the gas to flow outside. The inventors of this application previously applied for a patent directed to a gas generator having the construction of preventing the slag in gas from flowing outside even when the gas pressure rises instantaneously (Japanese patent application No. Hei 8(1996)-207929).
Specifically, the previously proposed gas generator has, as shown in FIG. 3, a housing 33 composed of an upper container 31 having a side cylinder 31b having a plurality of gas exhaust openings 38; an upper cap 31a closing an upper end of the side cylinder 31b; and a lower cap 32a closing a lower end of the side cylinder 31b. The housing 33 includes therein an igniter 70 having an ignitor element and an inflammation agent 72 sealed by barrier 35, gas generating agents 36, and a cooling/filtering member 37, which are arranged in this order from the center of the housing to a radially outside thereof. The cooling/filtering member 37 is formed to extend from the side of the upper cap 31a to the side of the lower cap 32a.
Further, the housing 33 has therein metallic foil 39, bypass preventing members 45, 46 and sealing members 40a, 40b. The metallic foil 39 adheres on an inner wall of the side cylinder 31b to cap the gas exhaust openings 38 from the inside. The bypass preventing members 45, 46 are provided at the opposite ends of the cooling/filtering member 37. The bypass preventing members 45, 46 have a L-shaped section, contacting with an inner surface of the cooling/filtering member 37 at the opposite end portions thereof and with inner surfaces of the upper and lower caps 31a, 32a. To ensure the effect of preventing the slag from flowing outside, the sealing members 40a, 40b are provided at end surfaces of the cooling/filtering member 37.
With the gas generator thus constructed, even when the gas pressure in the housing rises instantaneously to inflate the housing, since the bypass preventing members 45, 46 are located at the opposite ends of the cooling/filtering member 37, the slag in the gas can be prevented flowing outside. However, disadvantageously, the gas generator thus constructed has more parts and thus increased costs, due to the provision of the bypass preventing members 45, 46. Particularly in the circumstance in which specs on air bag systems are being standardized, cost reduction is being increasingly requested for gas generators, so cost increase resulting from the increase in component count is a significant drawback.
Accordingly, it is the object of the present invention to provide an improved gas generator at a low cost by improving the construction of inner surfaces of the upper and lower caps 31a, 32a to produce the function that is equal to or better than the function of the bypass preventing members 45, 46 of preventing the slag in the gas from flowing outside through the cooling/filtering member 37, thereby eliminating the need of the bypass preventing members 45, 46 to provide reduction of component count and a resultant improved efficiency in assembling work.